Conventionally, a specific autonomous sensor is mounted on various in-vehicle devices, especially on vehicle controllers for sensing vehicle's behavior information. As an example, a car navigation apparatus uses a dead reckoning navigation method. This method detects vehicle's position, bearing, speed, and the like using outputs from a relative bearing sensor such as a gyroscope, a steering sensor, a wheel sensor, etc. and a distance sensor such as a vehicle speed sensor, a wheel speed sensor, etc. The relative bearing sensor detects vehicle's bearing variations. The distance sensor detects vehicle's speeds (distances). These autonomous sensors make it difficult to calibrate characteristics changes due to individual sensor differences, environmental changes, and aged deterioration. The autonomous sensor has been thereby used merely as an ambiguous information input unit dependent on characteristics of the sensor itself. For example, the car navigation apparatus, one of in-vehicle devices, causes an error because outputs (position, bearing, speed, etc.), from the dead reckoning navigation, contain a sensor error. Since, in particular, positions and bearings are integrally obtained, errors increase gradually.
If a navigation apparatus has a GPS-based calibration function, the GPS is used to calibrate autonomous sensors. Accordingly, it is possible to calibrate characteristics changes in various autonomous sensors and accurately calculate various vehicle behaviors.
On the other hand, information from the GPS is used for vehicle controllers other than the car navigation apparatus. For example, the GPS provides the vehicle's absolute position. This position determines a traveling environment. Based on this traveling environment, vehicle's traveling state is controlled. That is to say, there is provided one or more pieces of various information about the traveling environment such as which road the vehicle is traveling, which latitude, longitude, and height correspond to the traveling location, and how the road is conditioned ahead. This information can be used to reflect the traveling environment on control of driving and traveling states in control systems for vehicle's wheels, traveling, and engine (e.g., see patent document 1). It is also known that the GPS information is used to learn neutral positions for sensors such as steering sensors and yaw-rate sensors that obtain measured values by assuming the vehicle's straight movement to be a neutral position. Such sensor uses GPS-generated vehicle's positions and map database to calculate a curve radius R for a route where the vehicle is traveling. Based on the curve radius R, the sensor determines whether the traveling route is straight or curved. Based on the determination result, the sensor learns the neutral position (e.g., see patent document 2).
[Patent Document 1]
JP-A-H6-324138
[Patent Document 2]
JP-A-2000-214180
However, the car navigation apparatus is disposed in a dashboard together with the other many devices and structures. Generally, the car navigation apparatus is mounted slantwise against the vehicle's horizontal direction. That is to say, attaching importance to the layout necessitates relaxing the installation requirements. Consequently, the car navigation apparatus cannot provide its original accuracy.
On the other hand, the use of GPS is limited for vehicle controllers other than the above-mentioned car navigation apparatus. Based on the GPS-generated vehicle's absolute value, a user simply references the map data for understanding the current route situations. Accordingly, the above-mentioned situations basically remain unsolved. That is to say, the autonomous sensors make it difficult to calibrate characteristics changes due to individual sensor differences, environmental changes, and aged deterioration. The autonomous sensor has been used merely as an ambiguous information input unit dependent on characteristics of the sensor itself.